1. Field of the Invention
The present invention generally relates to the field of mobile wireless networking, and more particularly to a system, method, and apparatus for transmitting and receiving data in a mobile communications network.
2. Description of the Related Art
Communication networks, for example the mobile telephone network according to the GSM standard (Global System for Mobile Communication), enable communication connections to mobile stations of mobile subscribers via a radio interface. These networks use radio-based components that set up, maintain and dismantle by communications links by transmitting and receiving signaling and traffic information (e.g. in the form of speech or data) in both transmission directions via the radio interface. Mobile subscribers access the communications network by means of mobile stations, which can communicate in wireless fashion with radio stations (base stations) arranged in distributed fashion at the network side. These base stations are often configured into cellular systems.
Cellular systems are composed of interconnected neighboring xe2x80x9ccell sites.xe2x80x9d These cell sites operate low power facilities (facilities that function on low amounts of electric energy). The cellular telephone industry is limited to 45 MHz of spectrum bandwidth, which without frequency-reuse, would limit each cellular carrier to 396 frequencies or voice channels. In order to increase calling capacity, these low power facilities xe2x80x9creusexe2x80x9d frequencies on the electromagnetic spectrum. The manner in which providers organize, or xe2x80x9cconfigure,xe2x80x9d their cells is an important factor in increasing frequency reuse and establishing an area""s calling capacity. One such configuration is an xe2x80x9comni cellxe2x80x9d configuration, which is often used in rural areas. Cells in urban areas often use a sector cell configuration. The omni cell configuration uses omni-directional or whip antennas that emit signals in 360 degrees. Whip antennas do not lend themselves to frequency reuse as well as sector antennas. As a result, omni cell configurations are generally used in rural areas since these areas are sparsely populated and consequently do not need extra calling capacity. Urban areas, on the other hand, have denser populations and require additional calling capacity to accommodate the system""s greater number of users. The sector cell configuration provides this extra calling capacity by utilizing sector or panel antennas that divide the omni cell into three segments. The three segments use different frequencies, allowing greater reuse of the channels. Because they have the capacity to handle large volumes of calls, sectored sites are used particularly in areas near high vehicular activity such as freeways and major intersections. Although a cell site""s radius depends upon its surrounding topography and its capacity to handle calls, cell sites in rural areas generally have a radius between five and twelve miles, and cell sites in urban areas typically have a radius between two and five miles.
There are three basic types of cell sites. Coverage sites serve to expand coverage in large areas or in areas with difficult terrain and to enhance coverage for portable systems. These sites allow users to make and maintain calls as they travel between cells. Capacity sites serve to increase a site""s capacity to handle calls when surrounding sites have reached their practical channel limits. Transition sites are needed for frequency reuse. Antennas mounted on tall support structures sometimes create a problem in frequency reuse because they xe2x80x9cseexe2x80x9d everything and overlap into the next cell sites coverage area. In order to control frequency reuse problems, these tall structures must be removed and replaced by transition sites. Transition sites allow the cellular company to increase the capacity of calls and maintain coverage simultaneously.
Traditionally, cellular phones have utilized analog transmission signals. In the analog technology, voice messages are electronically replicated and amplified as they are carried from the transmitting antenna to the receiving antenna. A problem with this technology is that the amplification procedure tends to pick up xe2x80x9cnoise,xe2x80x9d sometimes making the message difficult to hear. In order to diminish this noise and to provide greater calling capacity per channel, the cellular industry has is transitioning to digital transmission signals. In the digital technology, voice messages are converted into digits (zeroes and ones) that represent sound intensities at specific points in time. Because natural pauses in the conversation are eliminated, more calling capacity becomes available from the same amount of spectrum, thus reducing the need for new sites. An added benefit is that the background noise that is generally heard in the analog system becomes inaudible. The graphic difference between the two technologies is that analog signals are transmitted as continuous waves while digital technology converts the analog signal to binary digits.
There are currently two popular forms of digital technology: time division multiple access (TDMA) and code division multiple access (CDMA). Both of these forms of digital technology attempt to provide multiple access over one frequency, or channel. While TDMA may increase calling capacity three to ten times over analog technology, CDMA may increase calling capacity by ten to twenty times. Cell phones have recently added wireless access protocol (WAP) to allow more digital functions such as limited Internet access. In 2001, G3 (third generation) cell phones are expected to appear. G3 cell phones should supersede current cell phones because G3 phones will be able to attain a data transfer rate of 144 Kbps (under ideal conditions). Bluetooth-enabled cellular phones are also due in 2001. As with personal computers (PCs) and personal digital assistants (PDAs), Bluetooth cell phones will let users wirelessly transfer data among other Bluetooth devices. Bluetooth is a hotly anticipated feature in the cell phone market. Bluetooth is designed to enable users to create their own local-area network (LAN) or personal area network (PAN).
All of these advances, together with the proliferation of the Internet, have increased the demand for seamless wireless digital messaging and Internet connections. While the above mentioned cellular systems work well in areas of relatively high population density (e.g., in metropolitan areas), they are not accessible in many areas of the world. One such area in particular are the transoceanic shipping lanes used by freight vessels. The crews and passengers of these ships are typically unable to utilize their cell phones, two-way pagers, wireless email appliances, or Internet browsers unless they are in a port.
While satellites do offer the possibility of a connection to land-based digital networks, the costs associated with satellite communications (e.g., both hardware and airtime) may render it too expense for some cost-sensitive commercial shipping and fishing vessels. This may particularly be true for xe2x80x9clow priorityxe2x80x9d uses such as personal emails between crew members and their families and recreational Internet browsing. Thus, an alternative system and method for providing digital communications and Internet access for ocean-going vessels is desired.
The problems set forth above may at least in part be solved by a system and method that are capable of using mobile stations that act as store and forward repeaters to provide network connectivity.
In one embodiment, the method for transmitting data in a mobile digital network may include first broadcasting a first interrogation signal from a mobile station that has a data packet that is ready to be transmitted. The interrogation signal causes any other stations within range to respond with a response-to-interrogation signal. The mobile station may then transmit the data packet to the responding station. Once the responding station has received the data packet, it may send a confirmation signal to the first station acknowledging that the packet was correctly received. Checksums, encryption, and error checking and corrections codes may be used to ensure that the packet is received correctly and securely. The receiving station may be configured to store the data packet for future transmission to one or more other stations in a similarly manner.
The network may include both mobile stations and base stations. Mobile stations may be configured to be installed on a number of different vehicles (e.g., ships, aircraft, trucks, automobiles, or buoys). The mobile stations may be concentrated to provide coverage to traffic proceeding along known shipping lanes.
The mobile station may be powered by batteries, solar panels, or from the power system of the vehicle in which the mobile station is installed. Mobile stations installed in floating buoys may be configured with extendable antennas to improve their range. To prevent damage in severe weather, the mobile station may be configured with a weather sensor (e.g., a wind speed sensor) that causes the antenna to retract if predetermined conditions are met.
Each mobile station may be configured with a unique address that is compared with the destination address of received data packets. If a received data packet""s destination address matches the mobile unit""s unique address, then the data packet has arrived at it""s final destination. The mobile unit may then transfer the data packet to an attached terminal or personal computer, or activate it""s own user interface to indicate that data (e.g., an email message) has been received. If the packet""s destination address does not match the receiving station""s unique address, then the receiving station may be configured to attempt to forward the packet to other stations. Note, even if no other stations are currently within range, the receiving station may be configured to store the packet until another station comes within range. Depending on the network configuration, this could be seconds (e.g., in the event of an aircraft coming quickly into range), minutes, hours, or days (e.g., in the event of a ship that has just passed into a remote area with no other ships having mobile stations within range. While networks that have large gaps in connectivity may not operate acceptably for activities such as Internet web browsing, non-real time activities such as email should nevertheless provide value those using the network. Advantageously, the use of costly satellite time and equipment may be avoided. In some embodiments, wireless transmission using cellular technology may be used.
In one embodiment, a mobile station for transmitting data in a mobile digital network may include an antenna, a transceiver coupled to the antenna, a processor coupled to the transceiver, a data storage memory coupled to the processor; and a power supply coupled to the processor and the transceiver. The processor may be configured to cause the transceiver to broadcast a first interrogation signal in response to receiving a data packet that is to transmitted. The processor may be configured to transmit the data packet in response to detecting a response-to-interrogation signal. The processor may also be configured to store the data packet in the memory and repeat the interrogation and transmission cycle until a destination-receipt signal corresponding to the data is received. The mobile station may also be configured to cause the memory to erase the data packet corresponding to a particular transmitted data signal for which the mobile station has received a confirmation-of-receipt message.
Different antenna configurations may be used based on the exact implementation (e.g., omni-directional whip antennas, or directional antennas such as dish antennas).
In some embodiment, the mobile station may be configured to determine whether the source of the response-to-interrogation signal has already received a copy of the data before transmitting the data in order to save power and/or bandwidth. The mobile station may be configured with a motor rotatably connected to the antenna, wherein the mobile station""s processor is configured to cause the motor to rotate the antenna (if a directional antenna is used). Note, rotation may include either the horizontal and/or vertical axis. The mobile station may also include a wind sensor coupled to the processor, and the processor may be configured to cause the motor to lower the antenna in response to detecting winds greater than a predetermined threshold.
The mobile station may also include a global positioning system (GPS) module configured to provide the processor with position and/or orientation information. This information may be shared amongst the different stations in the network (e.g., base stations and mobile stations) to allow for more efficient routing of data. Less expensive mobile stations may be configured with compasses to provide orientation information.
The network may include both mobile stations and base stations (e.g., with a traditional internet connection). The stations may be configured to act as store-and-forward repeaters. Also, the stations may be configured to purge data packets that are older than specified maximum age to prevent memory congestion or overflows.